Objectives: It is suggested that meticillin-resistant Staphylococcus aureus (MRSA) originated through the transfer of the mobile resistant determinant staphylococcal cassette chromosome mec (SCCmec) into meticillin-susceptible S. aureus (MSSA), and that the genetic background determines the stability of MRSA. To support this hypothesis, MSSA bloodstream isolates (BSI) in our hospital were characterised and the genetic background of the MSSA clones compared to endemic MRSA clones.

Methods: A random selection of MSSA BSI (n = 380), isolated between 1999 and 2006 in the University Hospital Maastricht (azM), were characterised with spa typing and the algorithm based upon repeat pattern (BURP). Furthermore, the prevalence of the virulence factors collagen adhesion (CNA), Panton-Valentine leukocidin (PVL) and toxic shock syndrome toxin 1 (TSST-1) was investigated.

Results: Up to 50% of the MSSA isolates had a genetic background common to the endemic MRSA clones, e.g. clonal complex (CC) 1, CC5. CC8, CC22, CC30, and CC45. Furthermore, several CCs not related to the endemic MRSA clones, such as CC7 and CC15 (12% and 7% of the isolates respectively), were observed. CNA, PVL and TSST-1 was observed in 42%, 2%, and 15% of the isolates respectively. CNA was associated with CC1, CC12, CC22, CC30, CC45, and CC121, while TSST-1 was associated with CC30.

Conclusion:

1Half of the MSSA isolates had a genetic background common to endemic MRSA clones.

2Several MSSA lineages, such as CC7 and CC15, were prevalent in our hospital.

3The prevalence of MSSA clones with genetic backgrounds both common and uncommon to MRSA clones, supports the observation that SCCmec is more stable in certain S. aureus genetic backgrounds.

4Although endemic MRSA clones could originated through the transfer of SCCmec into MSSA, it seems more likely that MRSA clones have been imported from abroad, rather than originated in The Netherlands.

Session Details

Date:

19/04/2008

Time:

00:00-00:00

Session name:

18th European Congress of Clinical Microbiology and Infectious Diseases